Symptoms of Ca and Mg Deficiency
Calcium deficiency — appears on young leaves: distortion and curling (Ca is immobile within the plant and cannot be redistributed from older tissue).
Magnesium deficiency — interveinal yellowing on older leaves (Mg is more mobile; the plant pulls it from older leaves to supply new growth).
Ca and Mg Antagonism
Excess calcium suppresses magnesium uptake. The optimal ratio is 3:1 to 4:1 by mg/L (150 mg/L Ca : 40–50 mg/L Mg).
When CalMag Helps — and When It Doesn't
Effective when:
- Using RO water (very soft source water)
- There is a clear magnesium deficiency on older leaves
- Growing in coco coir at the start of the cycle
Ineffective when:
- Source water is already hard — Ca and Mg are already sufficient
- Chlorosis on young leaves is caused by iron deficiency, not Ca/Mg
- The problem is antagonism from excess potassium
Three Mistakes That Cost the Most
- Adding CalMag at the first sign of any chlorosis without diagnosis
- Applying it without testing the hardness of the source water
- Increasing the dose when no improvement is seen
Signs of Correct Balance
Young leaves are normally shaped, older leaves are uniformly green, and the Ca:Mg ratio in the solution is 3:1–4:1.